1. Field of the Invention
The present invention relates to automatic power calibration apparatuses for optical recording devices and automatic power calibration methods therefor. More specifically, the present invention is directed to an automatic power calibration apparatus for optical recording devices and an automatic power calibration method therefor, which can perform automatic power calibration in an optical recording device without requiring a measuring apparatus for measuring an output of an optical emission unit like a laser diode.
2. Description of the Related Art
In recording media such as compact disc-read (CD-R) and compact disc-read write (CR-RW), a power calibration technique for optical recording devices has normally been applied to properly determine the size of each of a plurality of channel signals, which are input to a driving circuit for driving an optical emission unit, e.g., a laser diode, included in the optical recording device, based on an output characteristic of the laser diode, such that the laser diode maintains a uniform output.
FIGS. 1A and 1B are diagrams illustrating output waveforms of a laser diode for recording data in recording media. FIG. 1A illustrates an output waveform of the laser diode for recording data in CD-R. A read channel, a write channel, and an overdrive channel are applied separately or all together to a laser diode driving circuit to produce the output waveform shown in FIG. 1A. In order to form a pit with a more ideal shape on a recording medium, overdrive power is applied to the recording medium together with normal writing power during an initial irradiation stage. Therefore, light having a greater power than the normal writing power is emitted to change the phase of a recording layer of the recording medium.
Data is recorded in the recording medium during a period of outputting a read power together with a base power. FIG. 1B illustrates an output waveform of the laser diode for recording data in CD-RW. A bias power channel, an erase power channel, and a peak power channel are applied separately or all together to the laser diode driving circuit to produce the output waveform shown in FIG. 1B. A bias power is not used for an output of the laser diode shown in FIG. 1B. Data is recorded in the recording medium during a period of outputting an erase power together with a peak power, while data is erased during a period of outputting only the erase power. A power calibration technique is applied to adjust channel signal values applied to the laser diode driving circuit and thus determine an input current of a laser diode, such that an overdrive ratio of FIG. 1A and an epsilon (ε) of FIG. 1B are maintained to be uniform. The overdrive ratio is defined as an overdrive power/(read power+base power), and epsilon (ε) is defined as an erase power/(erase power+peak power+bias power). In general, the value of the overdrive ratio ranges from 0.1 to 0.25, while the value of the epsilon ranges from 0.4 to 0.65.
In an example of a conventional power calibration technique, an optical power meter, which is an apparatus for measuring an output of a laser diode, is used. The optical power meter is capable of measuring an output of a laser diode while varying each of a plurality of channel signals input to a driving circuit for driving the laser diode and storing collected data in a memory, and thus determining the size of an applied signal for each channel based on the stored data.
However, the foregoing method may be costly since it needs an expensive apparatus such as the optical power meter. Also, an adjuster should vary each channel signal and check an output value of an optical power meter every time the channel signal is varied. As a result, the entire process is less efficient and the time required for data extraction is increased.